1. What is a Weed?
Weeds in the Horticultural
Plant out of place?
Setting
Plant with undesirable characteristics?
Plant with undiscovered virtues?
David Fischer
Dane County UW-Ext Crops and
UW-
Soils Agent Or some other definition?
What is a Weed Seed Dormancy
Flowers/vegetables
Seed Dormancy
– Breeding has removed dormancy
Abundant seed production
– Seeds become less valuable if dormancy exists
Seed survival
Vegetative reproductive structures Weeds
Lack of beauty, has offensive odor – Dormancy allows weeds to survive harsh
environmental conditions
Toxic/ Noxious
– May have different levels of dormancy within
same plant
Seed Survival Seed Production
Flowers/Vegetables Flowers/Vegetables – few seeds per plant
– Several years under ideal storage conditions – Sweet corn, up to 1000
– Pumpkins, several hundred
– “Seedless” watermelon
Weeds
– Documented survival after 100 yrs of burial
Weeds
– Survival is possible with some species after
composting – Common purslane, 1,000,000+
purslane,
– Common lambsquarters, 100,000
lambsquarters,

2. Vegetative Reproduction Toxic/Noxious
Flowers/Vegetables Noxious
– Very few perennials – those that are very few – Weed by law
spreading root systems (Kentucky bluegrass) – Why?
Weeds Toxic
– Perennials with spreading vegetative structures – Hazardous to humans and/or domesticated
– Annuals when pulled stem re-roots
re- animals
– Tillage can propagate
Grass ID Chart
Poaceae
Grass Family
Desirable species tend to be perennial
Weedy species
– Many are annuals
– Perennials can usually be controlled culturally
Identification via ligule and auricle
Giant Foxtail Yellow Foxtail
Hairy Ligule, Hairy leaf surface Hairy ligule, long hairs at leaf collar

3. Large Crabgrass
Green Foxtail Membranous ligule, hairs on leaf blade
Hairy ligule, no hairs leaf blade
Smooth Crabgrass Barnyardgrass
Membranous ligule, few hairs on leaves NO ligule
Quackgrass Sandbur Downy brome
HAS auricle
Rounded stem, soft hairs
Flat stem, hairy ligule
Fused sheath

4. Polygonaceae Prostrate Knotweed
Grows prostrate, high salt tolerance
Buckwheat family
Key family ID characteristic
is an Ochrea
– Membranous structure found
at leaf nodes
Several common weeds
Wild buckwheat Japanese Bamboo
Red Sorrel Curly Dock Chenopodiaceae
Goosefoot family
Stems tend to have vertical lines
Also have beet, Swiss chard and spinach
Seed usually irregular shaped

5. Kochia
Common Lambsquarters Common near railroad tracks,
Resistant to many herbicides
Leaves covered with white mealy substance
Prostrate Pigweed
Amaranthaceae Very few hairs, thin leaves
Pigweed family
Monecious plants mainly, some dioecious
Most members have red tinge to underside
of plant
Celosia or cockscomb also in this family
Somewhat limited as pests in horticulture
Redroot Pigweed Smooth Pigweed
Dull leaf color, rough textured plant via small hairs
Shiny leaf surface – due to lack of hairs on leaf blades

6. Tall Waterhemp Carpetweed
New plant to WI, dioecious, glabrous
Prostrate growing
Leaves in whorls
Does not have
stiff hairs
Catchweed Portulacaceae
Bedstraw
Common purslane
Semi-prostrate
Semi-
Succulent leaves
growing
Prolific seed
Leaves in whorls
producer
Stiff hairs that
Stems will re-root
re-
catch clothing
Ornamental species
– Rose moss
Caryophyllaceae Common Chickweed
Lower leaves
Pink Family petiolate
Plant glabrous
– Opposite leaves
Common in
– Flowers parts in fives lawns
Annual
Flowers
– Carnation
– Baby’s breath

7. Mouseear Chickweed
White Campion or Cockle
Perennial
Leaves are sessile
Leaves opposite
Long hairs on plant
Soft hairs cover plant
Common in lawns
White flowers
Annual, biennial,
perennial?
Brassicaceae Yellow Rocket
Deeply lobed leaves
Shiny appearance due
Mustard family to lack of hairs
– Extremely common to WI
Flower parts occur in fours
Seed pods are a silique or silicle and contain
a false partition
All cole crops also in family
Shepherdspurse
Wild Mustard
Winter annual, forms rosette
Christmas tree shaped leaves
Triangular seed pod
Serrated leaf
edge
Kidney shaped
cotyledons
Dull appearance
due to leaf hairs

8. Field Pennycress Fabaceae
Usually a winter annual
Shiny leaf appearance
Leaf edges wavy
Almost a unique shade of
green for leaf color
Black Medic
Penny shaped/sized seed
Trifoliate leaf
pod
Annual, biennial, perennial
Common in some lawns
Family also contains pea,
bean, clover, lupine, soybean,
peanut
Oxalidaceae Euphorbiaceae
Yellow woodsorrel
Shamrock shaped leaf
Spurge family
Yellow flower
Found in lawns
Flowers create special cluster called
cyathium (compacted floral structure)
Several economically important members
Rather unique seed pod
– Tapioca or cassava
– Castor oil
– Natural rubber
– poinsetta
Prohibited noxious
Leafy Spurge Prostrate/Spotted Spurge
Plant contains white sap
Perennial
White plant sap
Found in fields, ditches,
Prostrate growth, annual, native
right-of -way
Found in sidewalk cracks

9. Velvetleaf
Malvaceae
Common in agronomic setting
Large seeded plant
Mallow family
Also called buttonweed,
Economic importance elephant ears, velvetweed
Leaves have soft velvet feel
– Cotton
May have offensive odor
– Hollyhock
– Hibiscus
– Okra
Tend to have rounded leaves and seed pods
that form a ring of seeds
Common Mallow Apiaceae/Umbelliferae
Carrot Family
Rounded leaves and stem
Seed pod will form a ring Many are biennials
May be confused with
Inflorescence is usually an umbel
hollyhock as a seedling
Important economic
Found in gardens, disturbed
areas – Carrot, parsnip
– Dill, caraway, parsley
– Celery, chervil
Important human safety
– Wild parsnip, poison hemlock
Wild Carrot Wild Parsnip
Aka Queen Anne’s Lace
Biennial
Contains psoralen
Common in disturbed areas, right of
a photosensitive chemical
way, road ditches
Biennial
Problematic to carrot breeders
Found in disturbed areas, right of
way, road ditches

10. Lamiaceae
Convolvulaceae
Mint Family
Morningglory Family Lavender, basil, coleus,
Morningglory, sweet potato oregeno, sage, thyme
Field Bindweed 4 sided stems
Prohibited noxious
vine, rare in horticulture
Ground Ivy
Common in lawns
Extremely diff. control
Prostrate growing
square stem
Eastern Black
Solanaceae
Nightshade
Nightshade/Potato Family
Economic members
– Pepper
– Tomato
Leaves commonly have
– Potato
holes
– Tobacco Underside of leaf black or
purple
– Petunia, nicotiana
Berries green to black,
Many species can be poisonous toxic
Common in gardens,
disturbed soil
Jimsonweed Plantaginaceae
Leaves have very strong
Bracted
offensive odor
Strong hallucinogen
Seed pods form a bur 1 to 2
Buckhorn
inches in diameter
Large white flower
Plant can exceed 5 ft tall
Blackseeded/broadleaf

11. Canada Thistle
Asteraceae Prohibited noxious weed
Perennial
Very few spines on stem
Among the largest of plant families
Usually purple flowers
Flowers made up of ray and disk florets or Dioecious
just disk florets
Limited food plants
– Endive, lettuce, chicory
Extensive ornamental list
– Sunflower, aster, dahlia, daisy, zinnia, etc
Plumeless
Bull Thistle
Biennial
Thistle
Rough hairs cover leaf surface
Older plants large stiff spines
Far from plumeless
Stem is covered in spines
Midrib of leaf has hairs on
underside
Problem of pastures
Common
Sowthistle ssp.
Ragweed
Several very similar plants Pollen is source of hay fever
All have yellow flowers Common in disturbed soils
White latex sap gardens, fields, flower beds
Leaves with small spines Monecious plant
One species perennial
Giant Ragweed
Leaf auricles larger on Spiny than
Annual

12. Common Dandelion Chicory
Common on road sides, right of ways
Biennial
Used in teas
History as being used as folk
medicine
Smallflower
Horseweed
Galinsoga
Rare in horticultural setting
ROUNDUP RESISTANT
Prolific seed producer
AKA quickweed
Extremely small seed
Rapid growth after germination
Common in gardens
Once established hard to control
White ray florets surrounding
yellow disk florets
Prickly Lettuce
Similar to sowthistle
Exception is spines on midrib and stem
Mayweed Pineappleweed

13. Pest Management Options
Goldenrod Western Salsify
Cultural
Mechanical
Biological
Chemical
Integrated Pest Management Cultural Control Options
Judicious use of all available options to Lawn
control pests – Mowing height
» Taller is better
Management is based on pest species
– Fertilization
» Optimum levels
Considers environmental, ecoloical, and
ecoloical,
economical aspects – Water
» Deep if done
Cultural Control Options Mechanical Weed Control
Garden
Flower beds and vegetable gardens
– Rototiller
– Proper fertilization
» Prior to planting
» Inter row spaces
– Mulch – Hoe
Lawn
– Proper planting time and spacing – Dandelion spade or knife
– Thatching
– Control insects and diseases – Plug aeration

14. Chemical Control Chemical Use
Safety is of utmost importance
Use is limited in home horticulture setting
Herbicides are the safest of the ‘cides’
‘cides’
Too many different species in small area
– Skin/eye irritation most common concern
Most successful if based on differences in Homeowner products safest of the herbicides
growth habit
– Annual or biennial vs perennial
Must READ and FOLLOW label directions
– Grass vs broadleaf
Label Precautions Preen(dinitroanaline)
Make sure species and use are listed Controls germinating seeds
i.e. may be labeled for lupines Not labeled for all plants growing in garden
or flower bed
– But not as cut flower
Labeled for crop as a transplant May not cause visible harm to plant
– But not for crop as a seed – However, not labeled due to incomplete safety
data
Flower beds (Preen) Weed and Feed’s (broadleaf)
Usually 2,4-D or triclopyr
2,4-
May slow growth of transplants
Growth regulators
Human safety of less concern
– Unless used as cut or dried flowers
Oldest of herbicide families
– Dates back to WWII
Cultural methods probably best option
– Mulch, fertilization, proper planting
Affects auxin production and regulation

15. 2,4-D Safety 2,4-D Cautions
Lower LD50 than many herbicides used by Pet and child safety
homeowners Can volatilize
Offset by low use rates on a per area basis – Injury other susceptible plants
» Grapes
As with all chemicals proper safety
» Cucurbits
important
» Ornamental flowers
Pets may react to treated areas or several
days
Glyphosate Glyphosate
Roundup, Ranger, Rodeo, etc Non-selective herbicide
Non-
– Different formulations
– Active ingredient is glyphosate No soil residual
Among the safest of all active ingredients
Additives still cause for human concern When should it be used?
Interrupts ESPS synthase
Why shouldn’t it always be used?
Why Use Glyphosate Why NOT use Glyphosate
Human and environmental safety No selectivity
Excellent control of a wide range of plants Overuse may result in tolerance or
resistance
Easiest product for homeowner use for
control of brush Some other products work better in specific
situations

16. Weed ID Resources

17. Dane County Extension Staff Dane County Extension Staff